Digital nonlinear video editors are sophisticated tools which assist in the development of creative audiovisual productions. For example, a digital non-linear editor allows individual frames or clips of video from one or more sources to be individually edited and assembled into an elaborate video production. Audio can be combined therewith and modified as desired to produce a complete audiovisual production. One such digital nonlinear editor is described in U.S. patent application Ser. No. 08/771,447, filed Dec. 20, 1996 and assigned to the assignee of the present invention.
In general, the various audiovisual devices connected to a digital nonlinear video editor operate independent of one another. For example, a videotape player and an audio player may each have modules with time counters associated therewith, but provide no way to synchronize the counter of one with the counter of the other. Alternatively, the video player may not directly possess a time counter, but instead may be arranged to work with frames of information intended to be serially displayed at a predetermined frequency. Moreover, the starting point for one device may be offset from the starting point for another. For example, the desired video information for a video clip may begin at one-hour on the videotape while the desired audio information begins at thirteen minutes on its tape. Lastly, the time required for one device to rewind and/or thread a tape and begin prerolling the tape to stabilize itself for playback may be entirely different from the time needed by another device, such as a device that stores its information in high-speed RAM.
As a result of these myriad problems and others, synchronization of the various devices is difficult to accomplish and maintain. However, to be of any real value, a digital nonlinear editor not only needs to start its connected devices precisely in synchronization, but must also be able to rewind, play and fast forward devices in regular, scrub, loop and step modes all while maintaining the precise synchronization. Moreover, in addition to synchronizing the various hardware modules, a desirable non-linear editor needs to provide a user-friendly interface which may include independent software modules, each of which also need to be precisely synchronized with each other and the audiovisual devices. A hardware-based device such as a black-burst generator provides a highly reference timing signal, but there is no way to get the devices to align with the signals.